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where to locate subpanel (stud spacing, surface vs. flush mount, etc.)

where to locate subpanel (stud spacing, surface vs. flush mount, etc.)

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Old 06-30-08, 03:08 PM
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where to locate subpanel (stud spacing, surface vs. flush mount, etc.)

I'm going to put a run of #6-3 romex from my main panel (but not connected to the panel) to my attached garage (currently being built) just in case I need it in the future, possibly for a sub panel. The garage will have finished walls, so I'm just going to leave the wire behind the drywall. There are two walls where I could put the wire, and I'm not sure which would be better, so I have some basic questions about how sub panels can be attached to walls and studs, and how wires can enter and leave them.

I can run the wire to a wall with 12" stud spacing, which I think is too narrow to put a panel between the studs. On this wall a surface mounted panel would be ok with me, but I'm wondering if I can I feed the wire in from the back of a panel -- my understanding is that I can't run the romex feeder cable exposed on the outside of the wall to go in the top of the panel. With a surface mounted panel, could I run branch circuits from the sub panel using metal clad cable on the surface of the walls/ceiling, to avoid doing a whole lot of fishing/drywall work?

Alternately, I could run the wire to a wall which has studs 24" on center. I think this is wider than typical sub panels. On this wall, I would not like to have anything sticking out from the wall, so I would need a flush mount panel. Could I just attach the panel to one stud, or do I need to frame around the panel? Is there any clean way to get metal clad cable out from a flush mounted panel to run on the surface of the wall?

Please let me know if one of these installations would be better than the other, or if either one is stupid/impossible. Thanks!
 
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Old 06-30-08, 03:43 PM
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Why not save the money on the copper, since you don't have a ready use for it and run 2" conduit from the panel (using sweeps, and not sharp turns) to a location to be determined later, capping both ends. That way you can run the new cable(s) at will and not have to put out the money now.
 
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Old 06-30-08, 08:18 PM
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A few things...

Running NM (Romex) on the exterior of the wall to the panel is generally permitted. I'm not sure if it's 100% to code, but I've seen dozens if not more where the wire is run neatly up the wall. I guess the idea is that you're not going to be stacking plywood in front of your panel against the wires... right?

If worse comes to worse and your inspector is a pain about it, you can sleeve them in EMT conduit the 2 or 3 feet up the wall, but again, I've never seen anywhere that this has to be done in a residential setting.

As for mounting the panel in the wall, you can leave a cutout above the panel with an access door (HD has those spring fit access panels that are real easy to use). This will simplify snaking and running wires in the future. If you're real good, you can just cut an extra inch or so at the top and the bottom of the panel, and fish the wires that way. The panel cover will cover up that extra inch or so.

As you said, 12" is too small for a standard sized panel. 24" is too wide unless you have exterior plywood or something to mount it to. If you have the walls open now, put in an extra 2x4 at 16" so you're all set for the future.

But for your real question as to surface mount or recess/flush mount - it's really personal preference, and how often are you really in the panel anyway.

Oh - and Chandler has a great suggestion... especially considering the cost of copper these days.
 
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Old 06-30-08, 08:31 PM
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Also consider what might be a firewall, and don't do anything that would require you to breach it.

Realistically, drywall removal and repair is not rocket science. It's easy and cheap. Don't go to great lengths just to avoid it.

If you do run the cable, be sure to leave more extra than you think necessary.

NM cable may not be run on the surface of drywall, except in completely inaccessible areas.
 
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Old 06-30-08, 09:15 PM
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The comment about the price of copper got me thinking -- the only 6 gauge in the house is to the oven, which will have a 40 A circuit, not the 50 A I want to have here. At first I thought they just used bigger wire than required, but I just realized that it's aluminum. Am I correct that #6 aluminum is not good for 50 A? What gauge would I need for 50 A if the wire is aluminum, would it be #4?

Thanks for all the helpful replies!
 
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Old 06-30-08, 10:03 PM
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Typically for 60 amp useage if you want to go with alum wire route you have to use #4 anyway.

For now run 1 1/2 inch PVC conduit and cap it off for now but make a note where it will be ended.

Now for subpanel size normally they are 14.5 inch wide [ will fit in 16 OC studs but i know there are 12 inch verison but they are only good for 6/12* circuits the most.


Most subpanel I installed in garages they are useally 16 space which it is the most common one I installed it but I can install other size if the owner of that place request diffrent size then I can do that ahead of the time.

But keep in your mind with the garage if your state is on 2008 codes everything in garage is required to be GFCI'ed incluiding the lighting circuit and GDO.

Merci,Marc


* 6/12 repsetive a 6 fullsized breaker or 12 twinner or duplex breaker [ I rather used full size breaker to advoid some issue with it ]
 
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Old 07-01-08, 07:56 AM
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Am I correct that #6 aluminum is not good for 50 A?
This is not so simple as a yes or no question. It depends on the type of load. What you can get away with for a cooking appliance may not be the same as what you need for a feeder. Home centers often post these charts of wire size and amps as if it was that simple, but it's not.
 
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Old 07-03-08, 02:43 PM
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Originally Posted by John Nelson View Post
This is not so simple as a yes or no question. It depends on the type of load. What you can get away with for a cooking appliance may not be the same as what you need for a feeder. Home centers often post these charts of wire size and amps as if it was that simple, but it's not.
You're right, it's not that simple. I just looked up the NEC, and I see that the answer depends on insulation type. This #6 cable is THHN, so I think it is ok. I don't know about load types, but the electrician says it's fine for a 50 A subpanel, and the NEC table says so too (actually it says THHN is good for 90 degrees C, which gets you 60 A for #6 aluminum) so I'm not going to worry about it.
 
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Old 07-03-08, 03:34 PM
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Originally Posted by bajinnova View Post
This #6 cable is THHN
THHN is not manufactured in a cable format, but that's beside the point because #6 copper is okay for a 50A panel in any modern form.

In most situations, copper #6 THHN conductors in conduit are good for 65A, and copper #6 cables like NM-B or UF-B romex are good for 55A.

actually it says THHN is good for 90 degrees C, which gets you 60 A for #6 aluminum) so I'm not going to worry about it.
The actual conductor insulation is rated for 90C, however the panels, breakers and various other terminations are only rated for 75 or 60, so the 90 column can rarely be used in practice. In conduit #6 aluminum THHN is limited to 50A, and in NM cables 40A.
 
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Old 07-05-08, 12:22 PM
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The jacket says "4 CDR AWG 6 COMPACT AL ALUMAFLEX TYPE SE CABLE STYLE SER TYPE THHN 600 V". I think I was using the term "romex" too loosely, but it is a cable and claims to be THHN.

I don't really care about 60 Amps (90 degrres C), but I would like to be able to do 50 A. I understand that the only way this is possible is if the main panel breaker and whatever I'm connecting to on the other end are both rated for 75 degrees C. For a subpanel, as I understand it (please correct if wrong) this won't be a problem as long as I select the right subpanel (probably one rated for 100 A or greater).

The situation has changed a bit -- the builder/electrician is going to connect the cable to a 50 A breaker in the main panel, and just run it to an outlet box with a blank plate in the garage, where it will lay dormant until I decide to do something with it. I assume/hope he is using a 50 A breaker rated for 75 degrees C. Is there any reason to think this is not the case (in other words, is it possible to get 50 A breakers rated for 75 degrees C, or are 75 C breakers only available for higher currents)?

Thanks for everybody's advice!
 

Last edited by bajinnova; 07-05-08 at 12:40 PM.
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Old 07-05-08, 12:32 PM
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Thanks for getting the cable info up and the SER is the key word.,, I know it is THHN/THWN type., However they are treated like Romex cable

6 Gauge compact alum that is good for 50 amp max anyway.

Merci,Marc
 
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Old 07-05-08, 01:41 PM
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50 A is what I asked for, so that's ok. But actually the MFR website lists 60A @ 90 C ampacity for this cable as well, but it says it is for ampactiy derating purposes (not sure exactly what that means).

I just looked in my current house (rental) and all the GE breakers in there say 60/75C, even the 15A ones (I didn't think to look in there at first as I don't have any bigger than 30A, and I was under the impression that only the bigger ones would be for 75C).

I assume my brand new panel will be ok with 75C (I read somewhere that old panels aren't rated for 75C so breakers are irrelevant). I don't know what brand it is. Are there any that don't make 75C 50A breakers? If not I should be all set.
 
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Old 07-05-08, 06:39 PM
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Since you have asked for a cable that will supply 50 amperes to a subpanel the electrician will (should) use a circuit breaker that is suitable for 75 degree C. termination.

I don't understand why you don't just go ahead and install the subpanel now. The cost of the panel is less than fifty dollars and you do not need to install any breakers until you have a need.
 
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Old 07-05-08, 08:48 PM
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Originally Posted by furd View Post
I don't understand why you don't just go ahead and install the subpanel now. The cost of the panel is less than fifty dollars and you do not need to install any breakers until you have a need.
It's simply a matter of what the builder will/won't do for me at this stage, since the 240 V 50 A service wasn't agreed upon at the outset (I will have a 240 V 20 A outlet, wired with #10 copper that can support 30 A, but after the fact I decided I should have gotten a little more just in case I want it in the future). I think the guy in charge of actually building my house is doing as much as he can without getting himself into trouble. If I had a bit more control of the situation I would of course do exactly what you suggest. I am pleased to at least be in a situation where I can put more circuits in the garage later without having to tear up any other part of the house to run wires.
 
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Old 07-05-08, 10:10 PM
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Originally Posted by bajinnova View Post
50 A is what I asked for, so that's ok. But actually the MFR website lists 60A @ 90 C ampacity for this cable as well, but it says it is for ampactiy derating purposes (not sure exactly what that means).

They will rate the ampacity at diffrent tempture rating but for normal wires we used either 60C or 75C and majorty of the romex wires they do have 90C rating but per code we only can used 60C rating [ few types can use the 75C rating ]

and the higher rating is used to derated in hot area like attic or near heat source that will really change the ampacity rating pretty fast if not paying attetion and the recent 2008 code did fix that on the larger feeder wires.

Merci,Marc
 
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Old 07-06-08, 11:28 AM
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Originally Posted by bajinnova View Post
The jacket says "4 CDR AWG 6 COMPACT AL ALUMAFLEX TYPE SE CABLE STYLE SER TYPE THHN 600 V". I think I was using the term "romex" too loosely, but it is a cable and claims to be THHN.
That SER cable listed is good for 50A as a subpanel feeder.
 
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